Dear Fodorites.
We are arriving at Heathrow on BA16 at 5.30 am on 2 Dec 08 [ business ]at Terminal 4 and need to connect to BA flight 0304 [ economy ]at 7.20 am Terminal 5 to Paris the same morning.
I am told if I advise BA staff from departure point [ Sydney Aus ] to check in our luggage as through luggage they should go through to Paris direct. Any advice? Enough time allowed? Do we still go through customs? Thanks all.

Your bags will be checked through, no problem there. Just check that they are doing so - but if it's all on one ticket it's not a problem. You get a bus from T4 to T5, which takes about 20 minutes. You go through security again, but not through customs. The connection time yo have is actually not a legal connection time at LHR - 2 hours is the minimum, but at that time of the day you should be fine.

In fact by december you should be arriving at T5 too, so no need to change. According to the BA website all flights will have transferred to T5 by the end of October. Keep an eye on their website for news.

You WON'T be arriving from Australia at T5 whenever you fly.

BA's long term plan is to move its Sydney, Singapore and Bangkok flights from Terminal 4 to the new, allegedly superduper, OneWorld hub at Terminal 3, where all Qantas flights will also arrive and depart.

Their current announcements are that this switch will happen on September 17 this year, though these timings do move round a bit. Connections from T3 to T5 are supposed to be more frequent than from T4 to T5.

HOWEVER, 110 minutes isn't at present a "legal" connection. If BA or Qantas have sold you this on one ticket, you'll be fine: if your incoming flight's late, you'll just be put on the next. BUT if you're doing this on two separately-booked tickets, and your incomer's late, you get stuck in a security queue or the inter-terminal bus gets lost (don't mock), you might be in the doodoo.

So on one ticket: no problem. ON two: book the next flight to Paris.

Thanks for the correction Flanner - I didn't know that. Youlearn something new every day as they say and it is still early today

Heathrow legal connection time is 120 minutes at this point - but in my (quite recent) experience - that works if you have only carry-on and trot (not walk) through the terminals. (As noted, you will stay airside - not have to go through Immigration - but you will have to wend your way to the bus stop, wait for the bus to the right terminal to show up, drive all round the airport, disembark and go through security again.)

If it's all one ticket it's their problem in terms of finance - but still your problem being stuck in Heathrow for who knows how long. If you can I would change to something with at least a 3 hour connection time - and only then if issued all on one ticket.

Thankyou all.
Flanneruk, The flights will be on two separate bookings. The Sydney - london leg booked with Qantas fequent flyer points, the London - Paris leg via BA internet site.
So, overall its best to be safe than sorry and book the 9.25 am flight to Paris.
Thankyou once again, its much appreciated.